A numerical study of wind stress curl effects on eddies and filaments off the northwest coast of the Iberian Peninsula

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A high-resolution, multi-level, primitive equation ocean model is used to examine the response to the particular conditions of anticyclonic (negative) wind stress curl and equatorward (upwelling favorable) winds along the eastern ocean boundary off the northwest coast of the Iberian Peninsula in the vicinity of the highly productive rias. A band of steady equatorward winds, which are uniform alongshore but contain zonal variability (i.e., anticyclonic wind stress curl), results in an equatorward coastal surface current nearshore and a poleward surface current offshore. In time, the currents become unstable and lead to the development of anticyclonic warm core eddies. In addition, cold core filament formation occurs in areas where the anticyclones advect the upwelled coastal water offshore. The results from the experiments support the hypothesis that wind forcing, particularly the combination of anticyclonic (negative) wind stress curl and equatorward (upwelling favorable) winds, is an important mechanism for generating opposing alongshore surface currents, anticyclonic eddies, and filaments off the northwest coast of the Iberian Peninsula. In a sensitivity study, the results from three numerical experiments are examined to understand, in a limited way, the dependence of the generation of the surface currents on the boundary conditions (free slip and no slip), the use of wind band forcing and the imposed wind stress curl distribution. Results show that, regardless of whether free-slip or no-slip boundary conditions or wind band forcing are used, opposing alongshore surface currents are generated. Because such currents do not develop when there is no wind stress curl, the opposing currents are generated by the anticyclonic wind stress curl.